your statement
Replaced the plugs and ignition wires - no change - plugs are sooty.
after replacement of the plugs how long does it take for them to get sooty?
when you are at idle.... and you rev up the engine, can you notice the engine cut out and run rough at idle too?
this may sound crazy and it should not account for the sooty plugs but sometimes if you have a bad motor mount it can cause similar condition about running rough when you put it in gear, usually it will clear up after you get moving.. so can a bad valve.......
does it back fire at all?